This description relates to power transmission and distribution, and, more particularly, to systems and methods for subsea high-voltage direct current (HVDC) transmission and distribution system.
As oil and gas fields in shallow waters diminish, producers are tapping offshore fields in deeper waters with oil installations that operate far below the surface of the sea. The typical equipment for such subsea oil recovery and production include gas compressors and various pumps for multiple functions. Electric variable speed drive (VSD) and motor systems are one way to power such equipment directly under the deep water. Therefore, the delivery of electric power from a remote onshore utility grid or power generation is important to secure a reliable production and processing of oil and gas in subsea locations. Typically, the transmission power requirement is approximately one hundred megawatts for medium to large oil/gas fields.
Alternating current (AC) transmission and distribution systems are sometimes used for delivery of power to subsea locations. Such systems typically deliver AC power from a platform or terrestrial location to a large subsea transformer through a large power cable. Power is transferred from the subsea transformer to subsea AC switchgear through another power cable. The subsea AC switchgear feeds AC power to one or more subsea VSDs through yet another cable. The VSDs each provide variable AC power to electric motors through a power cable. The connections between components in subsea AC distribution systems typically require wet mateable connectors, which are significantly more expensive than dry mateable connectors. Moreover, the electronic components in subsea VSDs generally cannot tolerate high pressures and must be placed in large, thick walled pressure vessels capable of withstanding the high pressures present at various depths of water while maintaining a substantially constant pressure within the pressure vessel. Further, as pump, motor, and distribution components increase in power, size and weight increases. AC transmission and distribution systems also face technical challenges, which become more significant when transmission distance is in excess of one-hundred kilometers. For example, the significant reactive power drawn from the distributed subsea cable capacitors restrains the power delivery capability as well as increases the system cost.